A push-button unit of this kind is disclosed in DE-OS No. 26 58 706. The round shafts of the buttons of this push-button unit are guided in tubular projections of the cover. The ends of the shafts are slotted and provided with locking noses, so that the buttons are undetachable after insertion. Below each button, a helical spring for restoring the buttons to normal is slipped over the projections of the cover. Resting against the underside of the cover is a spring plate from which all contact springs of the push-button unit are cut free. The contact springs are pretensioned against a printed-circuit board mounted at a short distance from the spring plate. In the normal position, however, the contact springs are kept away from the conductive pattern of the circuit board by means of an insulating member provided at each button shaft. Located below the printed-circuit board is a flat box which contains hinged flaps capable of being actuated by the buttons, a slide, and a microswitch serving as a common contact. The flaps deflect the movements of the buttons at right angles and transmit the movement to the slide, which, in turn, actuates the microswitch. The push-button unit thus belongs in that category of mechanical units in which the coding contact elements are individually associated with each button. Electrical connection is made directly upon depression of a button.
The object of the invention is to provide a push-button unit of this kind which is particularly flat and simple in construction. On the other hand, the push-button unit is to be codable for different signalling systems, namely d.c. code C, multi-frequency, and loop-disconnect, and exchangeable for push-button units of another kind. This object is achieved by the features set forth in the characterizing part of claim 1. Preferred embodiments are apparent from the subclaims. The construction according to the invention fulfills the requirements to be met in an advantageous manner. The contact-spring strips permit manufacture involving little waste. The assembly of the push-button unit can be carried out with effortless ease or fully mechanized. The ease of changeability of the printed-circuit board and the small height of construction make the push-button unit suitable for many applications.